Status of the Theory of Isostasy. 



325 



These diagrams are based on the solution of 1909 

 which gave 113-7 kilometers, 70-7 miles, as the most 

 probable limiting depth under the hypothesis of uni- 

 form distribution. They are directly and accurately 

 comparable with each other, although, as previously ex- 

 plained, there is no especial importance to be attached 

 to the value of 70-7 miles. 



First, assume that the compensation is confined to a 

 stratum 10 miles thick. A couple of trial solutions 

 showed that to give the same minimum to the sum of 

 the squares of the residuals the bottom must be at a 



Fig. 5. 



-\01R 



\0ZR 



-*.03R. 



178.6 L|eo. 



Fig. 5. Several distributions of isostatic compensation which satisfy 

 equally well the deflection data, showing center of gravity of the dis- 

 tributions. 



depth of 37 miles, as shown in A of figure 5. The center 

 of gravity is consequently at a depth of 32 miles. 



Second, let this 10-mile stratum be expanded until its 

 top reaches sea level; the bottom will lie at a depth of 

 70-7 miles, shown in B. The center of gravity has 

 descended from 32 to 35-3 miles. 



Third, let the assumption be adopted that the amount 

 of compensation is a maximum at sea level and decreases 

 uniformly with depth until it becomes zero at the limiting 

 depth. This compensation, expressed graphically as a 

 triangle, is shown in C of figure 5. The limiting depth 

 is found to be 109 miles. 



